Aspirating plasma torch nozzle



:fl w 6 v, 31 Q E & & moss REFERENCE SEARCH ROOM 13, 1970 J. F. KIERNAN3,524,962

ASPIRATING PLASMA TORCH NOZZLE Filed June. 2, 1967 ATER I WATE W WPLASMA GAS OUT I 4 x I 35 48 11 HI m 40 I I 2 5O \43 76 82 [W2 a2 6 0 Lk PLASMA GAS WATER INLET WATER 3 3 OUT H -IW-DRAG x ml v H' I s D 88 8282 82 e4 GASIN I06 72 I04 INVENTOR 7 By JOSEPH F. K/ERNAN X W. QMAEX (MgATTORNEY 3,524,962 ASPIRATING PLASMA TORCH NOZZLE Joseph F. Kiernan,Dunellen, N.J., assignor to Air Re= duction Company, Incorporated, NewYork, N.Y., a corporation of New York 1 Filed June 2, 1967, Ser. No.643,151 Int. Cl. B23k 9/16 US, Cl. 219-75 4 Claims ABSTRACT OF THEDISCLOSURE BACKGROUND OF THE INVENTION Field of the invention Theinvention relates to electric torches for cutting metal plates or otherworkpieces, and more particularly to a nozzle for a cutting torch bymeans of which a shield of gas is caused to surround the plasma streamformed by the torch.

It is well known in the prior art to have a plasma torch with a nozzlein which a gas designed to form a protective sheath around the plasmastream of the torch is introduced under significant pressure into theinterior of the nozzle at a place relatively close to the orifice of thenozzle and the force of the stream of sheathing gas serves to aspirateair into the nozzle at the end remote from the orifice, with the resultthat the aspirated air comes in immediate contact with the very hot arcelectrode at a place where the air can chemically and physically attackthe electrode and contribute to rapid destruction of the electrode.

SUMMARY OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is afragmentary elevational sectional view of a cutting head including anozzle for aspirating air in accordance with the invention, the cuttinghead being shown in operative relationship to a workpiece;

FIG. 2 is a fragmentary elevational sectional view of a preferred nozzlefor aspirating gas from storage; and

FIG. 3 is a diagram illustrating the manner of measuring the drag of acut.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, the torchillustrated is of the general type disclosed in my copending applicationSer. No. 585,528, filed Oct. 10, 1966, assigned to the same assignee asthe present application. However, other torch forms may be used instead,and the invention is to be understood as not limited to the torch formillustrated.

With particular reference to the present invention, an

3,524,962 Patented Aug. 18, 1970 annular recess 72 is provided for thepurpose of surrounding the plasma stream with a gaseous sheath of air orother gas, particularly a gas which serves as an oxidizing agent tofacilitate the cutting operation or for other purposes. To useatmospheric air as the oxidizing or shielding agent a plurality ofpassages 82 are provided extending from the recess 72 to the ambientatmosphere. To use another gas for example from a storage vessel (notshown), a tip nut 50 may be extended downward as shown at 88 in FIG. 2to surround the exterior openings of the passages 82. An annular passage90 may be provided within the portion 88 interconnecting the passages82. A conduit 84, shown provided with a valve 86, is connected to thepassage 90. The gas is admitted to the passages 90 and 82 when the valve86 is open.

When the torch is in operation, the force of the plasma stream aspiratesair into the recess 72 through the passages 82 directly in theembodiment shown in FIG. 1, or other gas through the conduit 84 andvalve 86 as shown in FIG. 2, in either case to surround the plasmastream as it emerges from the nozzle to perform the cutting operation.

As shown in FIGS. 1 and 2, I prefer to use a plurality of aspiratingpassages 82, e.g., eight arranged symmetrically about the circumferenceof the nozzle. Also, I find it is advantageous to make the insidediameter of the bore 74 larger than that of the bore 70, to accommodatean increased volume of gas resulting from the aspirating action.

Certain cooperating portions of the torch will now be describedincluding, within a tip nut 50, a metallic head 1 of substantiallycircular cylindrical form, which is traversed by respective holes 8 and9 displaced from its axis in opposite directions in the plane of FIG. 1and parallel to the axis. From enlarged mouths of these holes thereextend respective metallic tubes 10 and 11 whose end portions may bebrazed to the head 1.

The head 1 is provided with an axial bore, the lower portion 2 of whichmay have a diameter somewhat less than the separation of the holes 8 and9 from each other, and the upper portion 3, of which bore is of somewhatfurther reduced diameter.

Within the bore 3 there is fitted a spacer number 60, preferably made ofa suitable ceramic material, and having a bore 62 concentric with thebore 3.

Centrally supported within the bore 62 is an electrode holder 31,illustrated as externally threaded at 48 to provide a path within thethreads to impart whirling motion to a stream of gas. Alternatively,instead of external threads on number 31, internal threads may beprovided in the spacer 60 to produce the whirling. Centrally fittedwithin the member 31 is an electrode 35.

A nozzle member 40 is supported within the bore 2 in the form of agenerally spool-like metallic member coaxial with the spacer 60,electrode holder 31 and electrode 35. The nozzle 40 has an upper port 41into which the electrode 35 may extend slightly as illustrated. Belowthe port 41 there extends a truncatedly conical bore 43, a straight bore70, and the annular recess 72.

The function of the electrode 35 is to serve as one terminal, typicallythe cathode, of an arc stream having the form of an intense andconstricted ionized gas plasma which issues from the torch and by which,as is known in the art, various functions such for example as cuttingmay be usefully performed. A purely illustrative example of the gas is amixture of 90% nitrogen and 10% hydrogen. The shape of the contour ofthe plasma stream is indicated schematically by broken line 76,extending into a kerf 78 in a workpiece 80 upon which workpiece acutting operation is illustrated. Gas to form the plasma may be suppliedin the space between the spacer 60 and the whirler 31. Coolant, e.g.,water, to cool the nozzle 40 9 a may be fed into tube 10 and drawn outfrom the tube 11.

In successful tests of a nozzle embodying the invention, I have beenable to cut metal plates at greater linear speed with a givenexpenditure of power, and to cut at ordinary speeds with reduced power.In cutting one inch thick mild steel plate I attained a cutting speed of36 inches per minute with an aspirating nozzle embodying the invention,as compared with 30 inches per minute using the best available prior artnozzle. The power required when using the prior art nozzle was about 101kilowatts as compared with about 87 kilowatts when using the nozzleembodying the invention.

In cutting one inch thick aluminum plate I attained a cutting speed of80 to 85 inches per minute compared to 70 inches per minute with a priorart nozzle. These nozzles had a throat diameter at the narrowed point of0.187 inch. With other nozzles having a throat diameter of 0.161 inch, Iattained a cutting speed of 50 to 60 inches per minute compared to 40inches per minute with a prior art nozzle.

In every case, the edges of the cut piece were consistently more nearlyvertical using the nozzle embodying the invention than when using aprior art nozzle.

Use of the invention also reduced the drag encountered in making a cut.FIG. 3 shows how the drag is measured. One face of the cut is shown at100 and the uncut portion of the plate is shown in section at 102, withthe freshly cut contour shown at 104. The plasma stream is shownschematically at 106. The drag is measured parallel to the upper andlower plate surfaces between the upper and lower extremities of thecontour 94. In practice, the measurement is made by stopping a cut inprogress and measuring the drag when the plate has cooled.

While illustrative forms of apparatus and methods in accordance with theinvention have been described and shown herein, it will be understoodthat numerous changes may be made without departing from the generalprinciples and scope of the invention.

I claim:

1. In a plasma torch, in combination, a nozzle means having a passagewaytherethrough including a restricted part, means to generate a plasmastream and direct the same through said nozzle passageway, aspiratingmeans located beyond the downstream end of the restricted part andoperated by said plasma stream, said aspirating means comprising aconnection means between the ambient atmosphere and the surface of saidpassageway.

2. Apparatus according to claim 1, in which said connection from theambient atmosphere to said nozzle passageway beyond the downstream endof the restricted part extends substantially perpendicularly to thecentral axis of said plasma stream.

3. Apparatus according to claim 1, in which said aspirating meansfurther comprises a portion of the nozzle structure forming an enlargedbore concentric with the central axis of the nozzle passageway.

4. Apparatus according to claim 3, in which said connection runs fromsaid enlarged bore and extends substantially perpendicularly to thedirection of said central axis.

References Cited UNITED STATES PATENTS 2,982,845 5/1961 Yenni et a1.219-74 X 3,042,830 7/1962 Orbach 2l9121 X 3,082,314 3/1963 Arata et a1.21975 3,104,310 9/1963 Moss 219--75 3,304,402 2/1967 Thorpe 219121 X3,387,110 6/1968 Wendler et al. 219-121 X.

JOSEPH V. TRUHE, Primary Examiner C. L. ALBRITTON, Assistant ExaminerU.S. Cl. X.R. 2l9--121

